Means for recording and reproducing sound



Feb. 20, 1923. 1,446,246.

v L. DE FOREST- MEANS FOR RECORDING AND REPRODUCING SOUND.

' FILED SEPT 18, 1919. 2 SHE ETSSHEET HII Feb. 20, 1923. L. DE FOREST.

MEANS FOR RECORDING AND REPRODUCING souwo.

2 SHEETS-SHEET 2.

' FILED SEPT 18,1919.

L m ATTORNEY reproduction thereof.

Patented e. 20.1923. v a i nnn DE ronns'r, or nnw yonn, n. Y.

means non nnoonnrns AND nnrnonncmo scum).

Application filed September is, 1919. Serial No. 324,683.

To all whom it may concern:

Be it known that 1, LEE on Foster, a citizen of the United States, residin New York, county and State of New ork,

5 have made a certain new and useful Invention in Means for Recording and ideproducing Sound, of which the following is a specification. f

This invention relates to making a record 10 of sound waves and to reproducing the same from the record somade.

The object of the invention is to provide an electrically operated means for recording and reproducing recorded sound.

A further object ofthe invention is to provide a novel form of sound record.

A. further object of the invention is to provide a simultaneous recording of sound waves and light waves and the simultaneous A further object of the invention is to provide a photographic film having recorded thereon photographs and sound record.

A further object of the invention is to simultaneously reproduce from such photographic film. the sound record and the pictures or negative'developed thereon, or, in other words, to reproduce talking moving pictures from a single roll of film.

Further objects of the invention will appear more fully hereinafter.

The invention consists substantially in the construction, combination, location, and relative arrangement ofparts, all as will he to more fully hereinafter set forth, as shown by the accompanying drawing and. finally pointed-out in the appended claims.

Referringto the drawin Fig. 1 "s a' diagrammatic'illustration of 4c a'sound recording arrangement embodying my invention. 5 i

Fig.2 is a similar view showing a sound reproducing arrangement embodying my in- '-vention. Figs. 3 and d-illustrate med forms of sound rec ords obtained. in accordance with my invention.

Fig. 5 isa diagraatic view showing" an j-autoniatic means for reproducing the sound from its record and for simultaneously controlling the intensity of volume or pitch thereof.

Fig. 6 is a $1 an view showing a modified light source;

many ways. that a source of light may be directly conrays pass through a lens in the usual well the Kun'tz variety are obtained by using :1

- this may be effected in many difi'erent ways The same part is designated by the same reference character wherever it appears throughout the several views.

It is among the special purposes of my present invention to record sound waves upon a photographic film such as an ordinary film employed in motion picture photography. This can be accomplished in l have discovered, however,

trolled bythe intensity, pitch and volume of sound in such. a manner that the fluctuations caused by sound waves in the intensity of light emitted from the source may be photographed upon the film. My investigations have revealed that certain light cells are more sensitive to the ultra violet rays of the spectrum than others.

l have shown and described in detail in a companion application Serial N o. 32%,685 filed on even date herewith a number of eflicient means for controlling electric currents by means of light variations for any purpose, and in'accordance with this invention I provide a source of light. for example, a lamp 1, the filament or incandescent electrode of which may be lighted to its sensitive or critical point of incandescence by means of any suitable source of current, for example, battery 2. The light known manner 3, and, if desired,a color filter d, which color filteris preferably of a dark blue, as I have found that the best results when using a photoelectric cell of filter of this color. A photographiofilm is passed by the lens and filters 3' and 4: in the usual well known manner, and the light emanating from the lamp 1 is'recordedi on the film, preferably in the nature of a minute ray obtained through a pin point a erture or focused to a ointby' a lens. Jae lamp 1 is controlled directly by and in accordance with sound waves, and while um I 'have'illustrated for the purposes or? this application 'a. simple 'microphone circuit comprisinga transmitter or microphone '5, included in a'closed circuit with a source of currentfi, the lamp circuit and the micr'ophone circuit being inductively "associated with each other through transformercoils 2.- With. this armentsound waves m the microphone set up weak pulsating currents which efli'ect the closed circuit of the lamp 1 and thereby cause light 'variations which elfects variation in intensity of light supplied to the sensitized surface of the film and thereby recorded. on the film in the form'of varying light exposures. In F ig. 2. I have shown a-simple arrangement for reproducing the sound waves from the recorded'waves on the film wherein the film 7 passes between a light sensitive electr cal device diagrammatically illustrated at 8 and a source of light 9 which is constant in intensity. device 8 may be anydevice of this nature, for example, it may be a selenium cell or a photo electrical cell, both of which I have found to be suitable for this purpose. It will be apparent that the. light that passes through the fihn 7 to affect the electrical devices 8 will vary inaccordance with the exposure on the film 7 and the fluctuating currents thereby set up in the circuit including the electrical device 8 will consequently vary directly in accordance with the original sound waves from which the sound record was produced. It will be obvious that the pulsating currents thus produced in the electrical? devices 8 may be converted in any well known manner back into sound waves either with or without previous amplification, and in my copendi-n'g application above mentioned I show various means for' reproducing with and without amplification the pulsating currents set up in the electrical devices 8 in the form of the original sound waves. The applications of the foregoing principles are many, and while I have shown and will now describe its application to motion picture photography to thereby obtain talking moving pictures? Iwish it to be understood thatI do not desire to be limited or restricted in this respect as this particular application has been selected for the purposes of illustration of the utility of the invention involved.

It is recognized that the great difiicul'ty heretofore encountered in the production of talking moving pictures has been the impossibility of obtaining perfect synchronism between the sound record and the picture in reproduction or projection. At a glance it will be apparent that I am enabled to simultaneously record or expose the film to the scene to be photographed and to the sound waves produced bythe talking, singing, or-

otherwise sound producing parts of the scene being photographed. By recording the sound waves and the light waves simultaneously on the same filni the problem of synchronism is obm'ously solved, for the sound waves, that is, their record. will be rep-roduced with the record of the light waves .at its prdper place in the projection or re- The light sensitive electricalproduction of the same. i It will thus be apparent that :I have provided-means which will enable making a permanent record not only of plays but ofall talking, singing, or other sound wave producing parts of the plays and enable the reproduction of the same with perfect synchronism inasmuch as they are on the same record or film in proper relation relative to each other. In

ig. 1 I show diagrammatically at 10 a motion' picture camera through which the motion picture film 7 passes intermittently in theusual well known manner. I rovide a suitable loop 11 in the passage 0 the film and on one side of the loop I subject the film to the sound controlled light, rays, the sound forcontrolling which is producedby the actors, musicians, or the like, which are being photographed, The loop which is provided between the sound recording devices and the camera or light recording. devices is to enable the film 7 to ass continuously by the-lens 3 as distinguis ed from the intermittent feedof the film past the camera aperture 3 for the obvious reason ofmaintaining the sound record as a continuous record. The relative speed of travel of the film 7 past the sound lens 3 and past the camera aperture 3 can easily be regulated in any well known manner, such as at present employed in the motion picture phoor the size of the exposure itself may be diminished in width to permit a narrow band along one edge to be. concealed when the corder. The film 7 passing by the reproduc- -scene exposure is made and exposed only 'when it reaches the sound controlled rei-ng mechanism, for example, as shown in Fig. 5, sets up currents in the electrical devices 8 in the manner hereinbefore described, whereby these currents are capable of conversion back; into sound waves. I have shown one arrangement for accomplishing this wherein I employ the audion of my invention indicated at 20,- which audion is used extensively in the wire and radio communication art and wherein the filament electrode 21 heated in the usual well known manner byv means of current source 22 is connected to one terminal of the electrical devices 8, the other terminal of which is connected with the grid electrode 24. The electrode 25 of the audion 20 is connected throughcurr'ent source 26 to the filament in the usual manner. In the arrangement shown I employ a'cascade amplifier or a combination detector and amplifier whereby the currents of the current variations inthe lnpu t or grid filament circuit of the audion '20 are amplified and conducted'through the of the variable elements in the audion circuits, for example, the current source 22 for supplying the current to the filaments of the respective audions can 'eflectively control the intensity of the outputcircuit of thelast audionof the series, and I therefore provide means whereby the film 7 on which the sound waves have been recordedin the form of light exposures passes by two reproducing devices adjacent to each other, theone device 8' fee,ding into the input circuit of 'the audion amplifier system and the other device 8 controlling the filament current. of theamplifier system to make'louder or softer or otherwise vary the intensity and pitch of .the reproduced sound waves'by and in accordance with the original sound record. This is accomplished for example by including the auxiliary electrical devices 8" in the grid filament circuit of audion 29, theoutput or'plate filament circuit of which includes a solenoid coil 30, the plunger of which is in the form of a rack 31 which meshes with a segment 32 which forms the control arm .33

of a rheost'at resistance 34; for controlling the filament current source 22. The foregoing arrangement is preferable to .the

modification shown in Fig. 4, and which ll will hereinafter describe in that the entire operation of the reproduction of the'sound is automatic in operation and relies solely upon the original sound waves? and the record thereof for controlling the intensity and pitch of the sound waves reproduced therefrom. It is possible, however, to arti ficially effect the volume or pitch or.in-=

tensity control on the film by means of an auxiliary '0! tone record 40 in a parallel line on'the film adj acent' the sound record 13 as illustrated in Fig. 4, the said artificial record 40 being made by the director or operator. after the simultaneous light and sound records have been made, in which case the auxiliary electrical devices Bwould obviously be placed out of alignment with the electrical devices 8 so that they would both simultaneously be affected.

With reference to the lamp 1 I will now describe a little more in detail several. forms frequenc ofdamp which lshav'e. found to be eficient for 'the purpose of supplyin a source of sound controlled'light; 1 fidd that a suitable source of light, the intensity of which is voice controlled,fconsists of a small incandescent'filamen't lamp,'p'referably of .25 to .50

amperes filament current; This filament should be very short, preferably from one eighth to one-sixteenth of an inch long, and

should be mounted 1 across two leading in wires of-relatively large cross section, and as short as possible inside the lam but leading out through the glass seal to a 0rd the maximum possible cooling or heat conducting facilities. It is highly important that the filament should be as smallas possibleand that every possible facility for conducting the heat away from the filament should be provided. I prefer therefore to use 9; nitrogen, or other gas filled lamp,'-to a high vacuum lamp. With such a lamp as described I find the degree of light variation by and in accordancewith the sound to be from four to five times that of a similar'low voltage small filament lamp but having the usualsmall lead in wires andevacuation. Moreover, the light from a nitrogen filled lamp is inuch richer in violet and ultra 'violet rays, which most actively affect both the photographic film and the photo-electric cell. I findt'h'at to'get the most sensitive voice control of the light from such a lamp it is important to have the filament normally lighted from a local source (whichmay be a batteryasabove described), and regulating the normal light thus obtained by means of. a rheostat in the usual manner in series with the said, source and the-secondary of the transformem inthe primary circuit of which is the microphone or voice controlled currents, as above explained. I therefore always use such a source of current in series with the secondary of a transformer and the lamp filament, and normallyburn the filament at the brilliancy found by trial to give the most sensitive response to the super-' imposed voice currentsn. place of the ahove described meandescent 1p method of controlling by sound waves the light intensity 1 may use a small arc lamp as shown in Fig. 6. Such lamp preferably consists of two heavy tungsten ball electrodes 50 and 51, separated by a small gap, for example, 0.5 millimeters, V 120 mounted in a" small lass vessel 52, either evacuated or filled with some gas, such as nitrogen, mercury vapor, etc, to make the light from such arc as rich as possible in ultra violet rays. ll energize such are froma source of high frequency current, the

aud ble imits, and modulate the high frequency currents supplied the arc lampwith alternating or pulsating currents set up by and 1n accordance with the sound waves.

of which must be well above the usual plate Foramp e; the gh tr q neri e r may be supplied the arc lamp by the oscil lion illustrated at' 602 and comprising the electrode 6'1; and grid electrode 62 interposed-between the plate and filament electrode 63. The grid and plate electrodesare connected by an oscillatgingcurrentcomprising transformer coil which is 'in--j ductively associated with the' transformer coil, 65', connected at its'terminals to; the. respective balls 50 and 51. I ,The condensers 66 are shunted around"inductance 64and a".

tap connection 67 is provided between. this oscillating circuit and' the filament electrode 63. The common oselllatin circuit'is-pro vided with a connection to t efilament-elee trode 63including impedance coil 68 and a source of current 69 shunted by a condenser 70. The foregoing is briefly a w'v'ell estab lished and now wellknown form of high frequency generation circuit forming the subject matter of separatepatents and applications. The alternating or pulsating currents produced b the microphone as hereinbefore describe are led to the input electrode of the audion amplifier 90, the output electrode of which leads'into 'the'filament and oscillating circuit tap 67 through the transformer 91,- as willbe readily understood, therebyefiecting' a modulation of the high frequency oscillations generated. by the.

balance 0f the oscillion system, and the modulated hi hfrequency oscillationsvary the. degree 0% brilliancy of light} emitted from the arc lamp bythe unmodulated highfrequency currents, which variations are proportional in ever respect to the original modulating audible requency alternating'or pulsating currents in the microphone circuit.

Many modifications and changes in details vvill readily occur those skilled in the art mew without departing from the. spirit and scope of m invention as defined in the cla' there ore whatI claim as new and useful an of my" owniinvention and" desire, to

by Letters Patents is,

I 1. The combination cally obtained sound record, 0 trolled by saidre'cord 01- producing an means can.

electric current yarying in potential in 'accordance with said record, an audion ampli fierfo'r amplifying said current, and a sound 'th at photographi- I producer controlled by theoutput circuit oi said audion, and means controlled by the record for controlling the. current supplied the filament ofsaid audion to thereby control thevolume of the sound producedby said producer. I .2. The combination with a photographicallyobtained sound record, of means for reproducing the sounds from the photographicrecord, and meanscontrolled by the record independently of the reproduction thereof for controlling the .volume of-sounds reproduced therefrom.

3. The-combination with a oto'graphically obtained sound record, 0% means con- LEE on FORESTQ 

